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I am currently designing an input selector module. I plan on using it in the 4S preamp I am currently building (see in the valve section of the forum). If my design reaches my expectations, I may build an other one in a separate enclosure. I have a mitsubishi da-p20 preamplifier that I really like, but it only has one "aux" input...

To make the question simple, I don’t know how to power my selector. My preamplifier mains power transformer has a 6.3v 2.5a heater supply, but it doesn’t have a center tap. On the other hand, I feed my preamplifier with clean 250VDC, but it’s way too much to power relays, LEDs and FETs.

With the added input selector board in the enclosure, space begin to be an issue so I need a simple solution with the fewest parts possible and/or the smallest footprint. Not having to run ac wires around the "signal side" of the preamp would give me more flexibility. DC heaters would then become an interesting way around this problem because the low tension supply could also be used to power my input selector, given that it’s powerful enough to power everything.

Is there something i am missing ? Any hint or information is appreciated !

Hi, You didn't specify what voltages and power you need. I often use DC to DC and AC to DC solid state converters to power similar things. Meanwell makes a bunch of them (Jameco carries them) and can do things like 120-240 VAC to 12 VDC, 8-18VDC to symmetrical +/- 12VDC and so on. 3, 5, 6,12 etc voltages are typical. They have input to output isolation as well. Most are regulated and they work quite nicely. A simple capacitor on the outputs is usually sufficient to insure no switching noise gets out.

I dont have a specific power/voltage need for the selector since I can build it to fit what is accessible. I need 1.6A at 6.3VAC for my heaters (EZ81, 12AX7 and 12AU7). My transformer (hammond 269ex) is rated for 6.3VAC and 2.5A.

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